Copy machine having photoconductive belt

ABSTRACT

An electrostatic copying machine for producing multiple copies of an original wherein several latent electrostatic images are formed on contiguous segments of a photoconductive surface on a moving belt supported by an air bearing. The belt is stopped for the exposing and developing (and, in one embodiment, image transfer) steps, and the scanning unit moves in opposite directions in successive copying cycles. Machine operation is controlled alternately by microswitches actuated by projections on the belt and by scanner-actuated microswitches. Three kinds of image transfer devices using pressure alone are disclosed, including one for which the belt is stopped during the transfer step.

United States Patent [191 Hastwell et al.

COPY MACHINE HAVING PHOTOCONDUCTIVE BELT Assignee:

Filed:

Inventors: Peter J. Hastwell; Ian E. Smith;

Dennis I. Scroggs, all of North Adelaide, Australia Savin Business Machines Corporation, Valhalla, N.Y.

Nov. 29, 1972 Appl. No.: 310,667

US. Cl 355/8, 355/10, 355/14,

References Cited UNITED STATES PATENTS Wright 101/1345 X Khoury et al '355/76 Ritzerfeld et al. 355/11 X Snelling et a1. 355/3 X McFarlane 355/4 Parmigiani.... 355/3 Westervelt.... 118/62 .Iugle 355/10 X Kakii et a1. 355/8 X Adelman, 355/3 R Sullivan 355/3 X Paull 355/16 Koizumi 355/8 Jordan 355/16 [111 3,836,245 [451 Sept. 17, 1974 3,740,132 6/1973 Komori et al. 355/3 R 3,743,408 7/1973 Ohno 355/10 OTHER PUBLICATIONS Bonafino et al., Air Transport, IBM Technical Disclosure Bulletin, November 1970, p. 1417.

Krause, Pressurized Corona Method for Transferring Developed Electrostatic Images, IBM Technical Disclosure Bulletin, July 1971, p. 582.

Bonafino et al., Guide Roll," IBM Technical Disclosure Bulletin; Vol. 13, No. 6, November 1970, p. 1418.

Primary Examiner-Samuel S. Matthews Assistant Examiner-Kenneth C. Hutchinson Attorney, Agent, or FirmShenier & OConnor [5 7] ABSTRACT An electrostatic copying machine for producing multiple copies of an original wherein several latent electrostatic images are formed on contiguous segments of a photoconductive surface on a moving belt supported by an air bearing. The belt is stopped for the exposing and developing (and, in one embodiment, image transfer) steps, and the scanning unit moves in opposite directions in successive copying cycles. Machine operation is controlled alternately by microswitches actuated by projections on the belt and by scanner-actuated microswitches. Three kinds of image transfer devices using pressure alone are disclosed, including one for which the belt is stopped during the transfer step.

10 Claims, 5 Drawing Figures COPY MACHINE HAVING PHOTOCONDUCTIVE BELT BACKGROUND OF THE INVENTION Electrostatic copying machines are known in the prior art in which an organic photoconductive imaging surface is charged and exposed to a light pattern derived from an original to be copied, then developed in a tacky toner and contact-transferred to copy material. An example of such a copy machine is disclosed in the copending application of Smith et al. for a Method of Contact Transfer of Developed Electrostatic Images and Means for Practicing Same, Ser. No. 155,108 filed June 21, 1971. Such electrostatic copy machines may, for example, utilize an organic photoconductor formed over the surface of a cylindrical drum which rotates past the several units which charge, expose, develop and transfer the desired image. In its operation, the machine will produce only one photocopy per rotation of the drum, and the processing units perform their operations only once in each cycle.

Our copying systememploys an endless belt whose outer surface is made of an organic photoconductor. The photoconductive belt is arranged to move over lat erally disposed rollers lying in a common horizontal plane. A rectangular support structure occupies the region between the upper and lower surfaces of the belt, extending between the two rollers. The opposing horizontal walls of this support structure, adjacent the inner surfaces of the photoconductive belt are perforated and diffuse air supplied to the hollow interior of the support structure. The photoconductive belt thereby floats on a virtually frictionless air cushion. Contiguous segments of the belt are sequentially charged, exposed, developed and have their developed electrostatic images contact-transferred to copy material in a continuous manner. As one segment of the photoconductive belt is being charged another segment is being developed, and as one segment of the belt is being exposed another is transferring its developed image to the copy material. Narrow spaces between the belts active segments are arranged to trip microswitches which energize the various processing units arranged in sequential order adjacent the periphery of the belt.

SUMMARY OF THE INVENTION One object of our invention is to provide an electrostatic copier for use with a photoconductive imaging surface.

Another object of our invention is to provide an electrostatic copier particularly adapted for multiple reproduction of an original.

Yet another object of our invention is to provide an electrostatic copier of very simple construction, great accessibility, whose moving photoconductive surface experiences virtually no friction and whose electrical power requirements are very low.

Still another object of our invention is to provide an electrostatic copier whose sequence of photocopy operations is controlled by the motion of its photoconductive surface relative to the processing units which produce the electrostatic copy.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings which form a part of the instant specification and which are to be read in conjunction therewith and in which like reference numerals are used to indicate like parts in the various views:

FIG. 1 is a schematic sectional view of one embodi ment of our electrostatic copier.

FIG. 2 is a schematic sectional view of another embodiment of our electrostatic copier.

FIG. 3 is a schematic sectional view of yet another (a third) embodiment of our electrostatic copier.

FIG. 4 is a circuit diagram showing a control circuit for our electrostatic copier.

FIG. 5 is a schematic illustration of an arrangement of punched control holes on an extended segment of out photoconductive belt.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 we have shown one embodiment of our photocopier, indicated generally by reference numeral 10, comprising a generally rectangular, opaque housing 12 in which we have arranged a conductive endless belt 14, having a photoconductive outer surface 20, to pass over conductive rollers 16 and 18 mounted for rotation on shafts 17 and 19. The belt 14 is oriented so that its upper and lower stands are generally parallel to the upper surface of housing 12. The belt is driven in the direction of the arrow A by a motor Ml (not shown in FIG. 1) which imparts rotational motion to the shaft 19 by means of an arrangement of gear wheels, chains and pinions, as will be more fully explained hereinbelow. Recessed onto the upper surface of housing 12 is a glass exposure window 22 on which the original is placed, image face down, for photocopying. A rigid or flexible opaque cover sheet is hinged adjacent one edge of the exposure window 22 and is normally placed over the original to shield it from ambient light and to prevent accidental displacement of the original during the transmission of an image of the original to the photoconductive surface.

We provide an optical scanning system, indicated generally by the reference character 26, comprising a pair of horizontally disposed parallel slide rails 28 fixed below the exposure window 22. The rails 28 support a carriage 30 for linear travel thereon. An endless drive chain 32 carried by sprockets 34 is connected to the carriage 30 and is driven by a motor (not shown) to 'reciprocate the carriage 30 along the rails 28.

The carriage 30 houses the optical system which exposes the photoconductive surface 20 to a light pattern derived from the original. As the carriage 30 advances along the rails 28, the optical system comprising a mirror 38, a lamp 36, a lens 40 and a mirror 42 is activated and the system sweeps across the face of the original, transmitting to the photoconductive surface a reflected light pattern derived from the original.

We provide a developing unit, indicated generally by reference numeral 43, positioned adjacent endless belt 14 so that an application instrumentaility such as an applicator belt 44 applies liquid to the photoconductive surface 20. In our embodiments, the endless applicator belt 44 is arranged to pass over rollers 46 and 48 mounted for rotation on shafts 50 and 52 respectively. The shafts 50 and 52 are positioned in a developer tank 54 containing liquid developer in which applicator belt 44 is partially immersed. The applicator belt 44 applies the liquid developer over the exposed segment of the photoconductive surface 14 'to develop the latent image contained thereon. An overflow trough 56 collects excess liquid developer flowing from the belt 44. An airknife 62 directs excess developer liquid from belt 14 to trough 56. A pipe 58 carries liquid from tray 56 back to the developer supply system (not shown). The supply system feeds developer liquid to an inlet pipe 59 leading into tray.54. The developer supply system may be of the type disclosed in the copending patent application of Smith et al. for Apparatus for Developing Electrostatic ImagesfjSer. No. 212,155, filed Dec. 27, 1971, now US. Pat. No. 3,789,794. The liquiddeveloper may be of the tacky toner type disclosed in the copenidng patent application of Smith et al for Method of Contact'Transfer of Developed Electrostatic Images and Means for Practicing Same, Ser. No. 155,108, filed Dec. 27, 1971. I

We arrange a shaft 64 to carry a roll of paper 66 or other flexible copy material onto which the developed image on the surface is to be transferred. A pair of pinch rollers 68 grasp the paper from the roll 66 and feed it past a blade 70 to a conveyor system indicated generally by reference character 72. Upon energization of a solenoid 71, a blade 70 cuts the copy paper to the proper length for receiving the entire developed image from belt 14. Theconveyor system 72 comprises a plurality of endless belts 73 passing over rollers 74 and 76 mounted for rotation on shafts 78 and 80 respectively. Paper delivered by the rollers 68 from the roll 66 is advanced by belts 73 intothe nip between a roller 82 and the portion of belt 14 on roller 16. Roller 82 is mounted on a shaft 84 to press the sheet of copy paper into contact with the belt 14. The finished copy leaves the housing 12 through a discharge slot 86. A lamp 88 preheats the copy sheet passing under it to enhance the adhesive affinity of tacky toner on the photoconductive surface for the copy sheet.

We provide any suitable means such as steel strips or the like (not shown) for holding the paper down on the belts 73. A length of paper is releasably held in position on belts 73 by means of a plurality of fingers 75 forward of the roller 74 and adapted to be moved out of the path of the paper as a developed image on belt 14 arrives at the image transfer location. At that time any suitable means such as a solenoid 77 is energized to move the fingers 75 to permit the paper to move into the transfer station. Owing to this operation it is not necessary precisely to synchronize movement of belts 73 with movement of the belt 14.

We arrange an endless cleaning belt 90 on rollers 92 and 94, respectively mounted for rotation on shafts 96 and 98. One of the shafts 96 and 98 is driven by any suitable means to move the belt 90 relative to the photoconductive surface 20 to remove residual toner still adhering thereto after the image has been contacttransferred to the copy sheet. Belt 90 may be formed of any suitable material which produces a scrubbing action on the surface of belt 14. The lower part of the belt may be immersed in clear carrier liquid in a. tank 99.

The belt 14 is further arranged .to traverse upper and lower walls 102 and 103 joined byhorizontally spaced l beams 104 to form two vertically disposed, horizontal surfaces 106 and l08'lying in parallel planes. Joined respectively to the longitudinal and transverse edges of cantilevered surfaces 106 and 108, and spanning the distance between them are side walls 110 and end walls 112, which together with surfaces 106 and 108 formoa generally rectangular housing 114. The walls 102 and 103 having surfaces 106 and 108are perforated. Compressed air which is supplied internally to the housing- 1 14 by way of an inlet 109 flows outwardly through the perforations in the upper and lower walls 102 and 103 to form air cushions between the surfaces 106 and 108 and the inner surface of the upper and lower stands of the belt 14. The air cushions reduce kinetic friction between the belt 14 and the surfaces 106 and 108, thus reducing wear. Additionally, it prevents liquid devel oper from contacting the support structure 114.

We adjust the tension in the belt 14 by the action of a tensioning mechanism 116 which extends the distance between the rollers 18 and 16 over which belt 14 passes. A crank arm 118, constrained to move in a quadrant 120, moves a cam 121 adjustably to position the bearing blocks of shaft 17.

The length of belt 14 and the relative orientations of the charger station, the exposure station, the developer station and the contact-transfer station about the periphery of the belt are selected so that at any one time, as one segment of the photoconductive surface 20 is being exposed another segment is being developed, and as one segment is being charged another is contacttransferring its latent image to a copy sheet. To accomplish this result the belt 14 is intermittently driven.

In FIG. 2 we have shown another embodiment of our invention which differs from the embodiment of FIG. 1 only with respect to the manner in which the copy medium 66 is brought into contact with the developed electrostatic image on the outer surface 20 of the photoconductive belt 14. In the embodiment shown in FIG. 2 the copy paper delivered by the conveyor system 72 is directed by a roller rotatably mounted on a shaft 122 to a space between a horizontally oriented platen 124 disposed in a plane parallel and adjacent to the photoconductive belt 14. The platen 124 is arranged to contact the developed image on the belt 14 as it passes over the surface of the platen, by actuation of a solenoid 125 which upwardly displaces the platen from its normal position. The copy sheet introduced between the photoconductive belt 14 and the platen 124 by the guide roller 120 is thereby lifted into contact with the developed electrostatic image on the belt 14. We arrange a pair of rollers and 132 respectively mounted on shafts'l26 and 128 to grasp the copy sheet following its contact with the developed electrostatic image and to deliver the copy sheet to the discharge slot 86 by way of a conveyor belt 134. It will be appreciated that in this form of our invention image transfer takes place while the belt 14 is stationary.

In FIG. 3 we have shown yet another embodiment of our invention which again differs from the embodi ments of FIGS. 1 and 2 only with respect to the manner in which the copy medium 66 is brought into contact with the latent electrostatic image on the photoconductive outer surface 20 of the belt 14. In the embodiment of FIG. 3 the copy paper delivered by the conveyor system 72 is directed by a roller 135 rotatably mounted on a shaft 136 to a space between a perforated surface 138 forming the curved wall of a one-quarter section of a hollow right circular cylinder 140 and the belt 14. Air is delivered to the hollow interior of the cylindrical section by a compressor (not shown) by way of a pipe 142. The air is diffusd outwardly over the curved surface 138 through the multiple perforations therein and forms an air bed which presses the copy passing between the curved wall 138 and the belt 14 into contact with the developed electrostatic image on the belt 14.

uous copy production at various stages so that any preselected number of copies, including a single copy, may be produced. We have coupled the operation of both the developer unit and the transfer unit of our photocopy machine to the operation of our exposure unit. Inasmuch as we have arranged out photoconductive belt to remain stationary during certain of the operations performed by the machine, the operation of longest duration, which is that of electrostatic imaging by exposure to a light pattern derived from the original, is arranged to control the other operations. With this arrangement, when the machine is started, the first four photoconductive belt segments which pass through the transfer unit bear no electrostatic image since they received no corona charge; the fifth segment to arrive and all those following will have been charged, exposed and developed. For this reason we must delay the delivery of copy paper to the transfer unit until the photoconductive belt surface bearing an electrostatic image arrives at the transfer unit. This delay in paper delivery is achieved by a counter whose operation will be explained hereinafter.

Referring now to FIG. 4, we have shown a control circuit for our belt copier, the main lines 200 and 202 of which are connected across an appropriate source of potential. In the operation of our machine a counter Cl is set to produce the desired number of copies. A push button PB is momentarily depressed to initiate the sequence of copying operations. Closing of switch PB sets the main counter C1 to at least a count of l or to a greater count set therein by a dial or the like. The counter C1 opens a normally closed gating circuit 212. Closing of PB further resets a divide-by-four network 208 the function of which is explained hereinbelow. It also completes a circuit through the counter to the relay winding IR and closes normally opened relay contacts 1R1 and 1R2. The closing of relay contacts 1R3 complete a holding circuit through contacts 3R1 to maintain the relay winding 1R in an energized condition. The circuits completed by the relay contacts 1R1 and 1R2 activate the belt-drive motor BM, the cleaning unit motor Cm and the paper cutting and transport unit. The belt-drive motor BM begins to move the belt surface toward the corona charging unit. The paper cutting and transporting unit draws the copy paper from the supply roll 66, cuts the copy paper to an ap propriate length for receiving the developed electrostatic image in the transfer unit, and delivers the length of copy paper thereto to await the arrival of the developed electrostatic image on the photoconductive surface of the belt 14. As the belt 14 moves toward the corona-charging unit the projection204 on the belt 14 closes a normally open microswitch MSl, which completes a circuit through the relay winding 2R and closes normally open relay contacts 2R1 and 2R2 respectively to energize the corona-charging unit K and to complete its own holding circuit through a normally closed 6 switch MS2..The belt segment moving relative to the corona charger receives a uniform electrostatic charge until projection 204 provided on the belt surface opens a normally closed microswitch MS2. The opening of the microswitch MS2, opens the holding circuit through the relay winding 2R and deenergizes the corona-charging unit K. The subsequent closing of the microswitch MS3 by a projection 206 on belt 14 energizes a relay winding 3R which closes normally open relay contacts 3R2, 3R3, 3R4, and opens normally closed contact 3R1 to disengage the belt drive motor and arrest the belts motion. It will be appreciated that the belt remains stationary during image transfer in the form of our invention illustrated in FIG. 2 in which the platen 124 is to be raised to effect the transfer. In the other forms of our invention, the transfer is effected in the course of movement of the belt 14.

Closing of the-contacts 3R2 complete a holding circuit for winding 3R through normally closed contacts 4R1. Closing of contacts 3R3 completes a circuit for the developer unit 43 and for the image transfer system wherein the platen 124 is employed. Closing of the contact 3R4 completes the circuit of a drive motor EM for the exposure unit through a pair of reversing switches RS1 and RS2. The position of the switches RS1 and RS2 is determined by the position of the carriage followig its last movement. That is, at each of its limits of travel, the carriage reverses switches RS1 and RS2 so that the motor EM will drive the carriage in the reverse direction on the next closing of the contacts 3R4.

In addition to the reversing switches RS1 and RS2 controlled by the movement of the carriage 30, we also provide respective left hand and right hand limit switches LL and RL which are momentarily actuated as the carriage approaches the respective limit positions. At the limit each of the switches is open. Closing of either of the switches LL or RL energizes a relay winding 4R to open contacts 4R1 to deenergize relay 3R at the end of the developing, image transfer and exposure operations.

As has been explained hereinabove, we do not wish to feed blank sheets of paper to the delivery slot 86 during the initial operation of the machine. For that reason, we do not energize the finger release solenoid 77 until after the first four operations of the exposure motor. Closing of contacts 4R2 in response to energization of winding 4R applies a pulse to a divide-by-four network 208 which had been reset by operation of push button PB and to a normally closed gate 210. After the fourth closing of contact 4R2 network 208 actuates gate 210 to pass the next pulse resulting from closure of contact 4R2 to the finger release solenoids 77 to permit a sheet of paper to move into the transfer location.

This pulse indicates that a copy has been made. We apply the output of gate 210 to the counter C1 to step it down one count. Each subsequent closure of the contact 4R2 will result in stepping counter C1 down one count until finally the desired number of copies have been made and the gate 212 is deactivated.

We also apply the signal resulting from closure of contact 4R2 to the gate 212 to reenergize relay winding 1R to restart the belt motor BM. It will readily be appreciated that this operation continues until the main counter C1 has been stepped down to zero.

While we have described one form of control circuit which may be employed to control the operation of our machine, it will readily beappreciated that a more sophisticated control can be devised to eliminate some of the unnecessary operations inherent in the machine. Further by way of example we have illustrated the relationship between projections 204 and 206 on belt 14 and the positions of the microswitches M1, M2 and M3 in FIG. 5. of the drawings.

In operation of our endless belt electrostatic copy machine, counter Cl first is set to the desired number of copies to be made. Push button PB is actuated to initiate an operation of the machine. First, the belt 14 steps through a certain distance in which an electrical charge is applied to the photoconductive layer on the belt by the corona 100. At the end of the application of the corona to that section of the belt, the belt stops and the exposure system is actuated to cause the carriage 30 to move, for example, from right to left as viewed in FIG. '1, to cause an image of the original to be translated to the charged photoconductive surface to provide a latent image. Following the exposure operation, the belt 14 is againstepped to carry the latent image to the developer station. At the same time, another charged area is at the exposure station and the exposure and developer units both are actuated to cause one latent image to be produced while the preceding image is being developed. Next, the belt makes another step and the developed image is at an idle station while another image is being formed and yet another image is being developed. Next, the belt moves through another step. In the form of our invention shown in FIGS. 1 and 3, the first developed image is at an idler station during this step and image transfer takes place as the belt is moving in the course of the next movement. In the form of our invention illustrated in FIG. 2, image transfer takes place while the belt is stationary and the copy is delivered on the succeeding step.

It will be seen that we have accomplished the objects of our invention. We have provided an electrostatic copying machine employing an endless belt having a photoconductive imaging surface. Our machine is especially adapted to produce multiple copies of an original. The belt carrying the photoconductive surface in our machine is supported for movement with aminimum of friction. Our machine requires relatively little electrical power to operate. It is simple in construction for the result achieved thereby. The operating parts of the machine are relatively accessible for maintenance and repair.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to'other features and subcombinations. This is contemplated by and is within the scope of our claims. It is further obvious that various changes may be made in details within the scope of our claims without departing from the spirit of our invention. It is, therefore, to be understood that our invention is not to be limited to the specific details shown and described.

Having thus described our invention, what we claim 1. An electrostatic copying machine including in combination, an endless belt having a surface carrying a film of photoconductive material, a charging unit for applying an electrostatic charge to asurface passing thereby, an exposure unit mounted for movement between limit positions and adapted to be actuated to translate an image of an original over an area of a stationary surface positioned adjacent thereto, a developer system adapted to be actuated to apply developer to a stationary surface positioned adjacent thereto over an area corresponding in size to said area, means for effecting transfer of a developed image from said belt to a length of copy material, means mounting said charging unit and said exposure unit and said developer unit and said transfer means at spaced locations along the length of said belt, means adapted to be actuated to drive said belt to move said surface successively past said units and said transfer means, means for actuating said drive means to move said surface successively past said units and said transfer means, means responsive to movement of said belt length to a position adjacent to said exposure unit for deactivating said drive means and for moving said exposure unit between said limit positions and for actuating said exposure'unit to translate said image over said area, means responsive to movement of said exposure unit for reactivating said drive means to move said length to a position adjacent to said developer unit, means responsive to movement of said belt for again deactivating said drive means with said area substantially in registry with said developer unit, and means for again reactivating said drive means to move said length toward said transfer means.

' 2.-A copy machine as in claim 1 including means providing-a cushion of fluid for supporting said belt over a major portion of the length thereof.

3. A copy-machine as in claim 1 in which said belt is generally horizontally disposed to form upper and lower generally parallel stands, means mounting said charging and exposure units in spaced relationship adjacent to said upper stand and means mounting said developing and transfer units in spaced relationship adjacent to said lower stand.

4. A copy machine as in claim 1 in which said exposure unit mounting means comprises a reciprocating carriage;

5. A copy machine as in claim 1 in WhICh said transter I means comprises means for bringing a sheet of copy material into intimate contact with an image on said belt, means for holding a sheet of copy material in escrow adjacent to aid contact means, and means for actuating said escrow means to feed a sheet of said copy material to said contacting means.

6. A copy machine as in claim 1 in which said belt driving means comprises a roller supporting said belt and in which said transfer means comprises a pressure transfer roller forming a nip with a portion of said belt on said support roller.

7. A copy machine as in claim 6 in which said means for feeding a sheet of copy material to said transfer unit comprises means for holding a sheet of copy material in escrow adjacent to said nip and means responsive to movement of a developed-image-bearing portion of said belt toward said nip for actuating said escrow means to release the sheet of copy material for movement into said nip.

8. A copy machine as in claim 1 in which said transfer means comprises a pressure platen, means mounting said platen for movement toward and away from said belt, and means for moving said platen toward said belt while said belt is stationary to carry a sheet of copy material on said platen into positive engagement with said belt, and in which said copy material feed means feeds a sheet to said platen.

ond limit position to cause the exposure unit when actuated to translate an image of an original over an area of said surface, a developer system for applying develop'er to a surface positioned adjacent thereto, means for effecting transfer of a developed image from said belt to a length of copy material, means mounting said charging unit and said exposure unit and said developer unit and said transfer means at spaced locations along the length of said belt, means adapted to be actuated to drive said belt successively past said units and said transfer means, means responsive to movement of said belt length on one operation of said machine for deactivating said drive means and for moving said exposure unit from said first limit position to said second limit position and for actuating said exposure unit to translate said image, means responsive to movement of said exposure unit into said second limit position on said one operation for reactivating said drive means, means responsive to movement of said belt length on another operation of said machine for deactivating said drive means and for moving said exposure unit from said second limit position to said first limit position and for activating said exposure unit to translate said image, and means responsive to movement of said exposure unit into said first limit position on said other operation for reactivating said drive means. 

1. An electrostatic copying machine including in combination, an endless belt having a surface carrying a film of photoconductive material, a charging unit for applying an electrostatic charge to a surface passing thereby, an exposure unit mounted for movement between limit positions and adapted to be actuated to translate an image of an original over an area of a stationary surface positioned adjacent thereto, a developer system adapted to be actuated to apply developer to a stationary surface positioned adjacent thereto over an area corresponding in size to said area, means for effecting transfer of a developed image from said belt to a length of copy material, means mounting said charging unit and said exposure unit and said developer unit and said transfer means at spaced locations along the length of said belt, means adapted to be actuated to drive said belt to move said surface successively past said units and said transfer means, means for actuating said drive means to move said surface successively past said units and said transfer means, means responsive to movement of said belt length to a position adjacent to said exposure unit for deactivating said drive means and for moving said exposure unit between said limit positions and for actuating said exposure unit to translate said image over said area, means responsive to movement of said exposure unit for reactivating said drive means to move said length to a position adjacent to said developer unit, means responsive to movement of said belt for again deactivating said drive means with said area substantially in registry with said developer unit, and means for again reactivating said drive means to move said lengtH toward said transfer means.
 2. A copy machine as in claim 1 including means providing a cushion of fluid for supporting said belt over a major portion of the length thereof.
 3. A copy machine as in claim 1 in which said belt is generally horizontally disposed to form upper and lower generally parallel stands, means mounting said charging and exposure units in spaced relationship adjacent to said upper stand and means mounting said developing and transfer units in spaced relationship adjacent to said lower stand.
 4. A copy machine as in claim 1 in which said exposure unit mounting means means comprises a reciprocating carriage.
 5. A copy machine as in claim 1 in which said transfer means comprises means for bringing a sheet of copy material into intimate contact with an image on said belt, means for holding a sheet of copy material in escrow adjacent to aid contact means, and means for actuating said escrow means to feed a sheet of said copy material to said contacting means.
 6. A copy machine as in claim 1 in which said belt driving means comprises a roller supporting said belt and in which said transfer means comprises a pressure transfer roller forming a nip with a portion of said belt on said support roller.
 7. A copy machine as in claim 6 in which said means for feeding a sheet of copy material to said transfer unit comprises means for holding a sheet of copy material in escrow adjacent to said nip and means responsive to movement of a developed-image-bearing portion of said belt toward said nip for actuating said escrow means to release the sheet of copy material for movement into said nip.
 8. A copy machine as in claim 1 in which said transfer means comprises a pressure platen, means mounting said platen for movement toward and away from said belt, and means for moving said platen toward said belt while said belt is stationary to carry a sheet of copy material on said platen into positive engagement with said belt, and in which said copy material feed means feeds a sheet to said platen.
 9. A copy machine as in claim 1 in which said transfer means comprises pneumatic means for moving a sheet of copy material into positive engagement with said belt.
 10. An electrostatic copying machine including in combination, an endless belt having a surface carrying a film of photoconductive material, a charging unit for applying an electrostatic charge to a surface passing thereby, an exposure unit adapted to be activated to translate an image of an original to a surface positioned adjacent thereto, means mounting said exposure unit for movement between a first limit position and a second limit position to cause the exposure unit when actuated to translate an image of an original over an area of said surface, a developer system for applying developer to a surface positioned adjacent thereto, means for effecting transfer of a developed image from said belt to a length of copy material, means mounting said charging unit and said exposure unit and said developer unit and said transfer means at spaced locations along the length of said belt, means adapted to be actuated to drive said belt successively past said units and said transfer means, means responsive to movement of said belt length on one operation of said machine for deactivating said drive means and for moving said exposure unit from said first limit position to said second limit position and for actuating said exposure unit to translate said image, means responsive to movement of said exposure unit into said second limit position on said one operation for reactivating said drive means, means responsive to movement of said belt length on another operation of said machine for deactivating said drive means and for moving said exposure unit from said second limit position to said first limit position and for activating said exposure unit to translate said image, and means responsive to movement of said exposure unit into said first limit position on said other operation for Reactivating said drive means. 